Medical sensor for reducing signal artifacts and technique for using the same

ABSTRACT

A sensor may be adapted to reduce motion artifacts by mitigating the effects of the tissue moving within the sensor. A sensor is provided with an elastomeric sensor body adapted to accommodate patient motion. Further, a sensor is provided in which the sensor cable is arranged to mitigate its pressure on a patient&#39;s tissue.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and, moreparticularly, to sensors used for sensing physiological parameters of apatient.

2. Description of the Related Art

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In the field of medicine, doctors often desire to monitor certainphysiological characteristics of their patients. Accordingly, a widevariety of devices have been developed for monitoring many suchcharacteristics of a patient. Such devices provide doctors and otherhealthcare personnel with the information they need to provide the bestpossible healthcare for their patients. As a result, such monitoringdevices have become an indispensable part of modern medicine.

One technique for monitoring certain physiological characteristics of apatient is commonly referred to as pulse oximetry, and the devices builtbased upon pulse oximetry techniques are commonly referred to as pulseoximeters. Pulse oximetry may be used to measure various blood flowcharacteristics, such as the blood-oxygen saturation of hemoglobin inarterial blood, the volume of individual blood pulsations supplying thetissue, and/or the rate of blood pulsations corresponding to eachheartbeat of a patient. In fact, the “pulse” in pulse oximetry refers tothe time-varying amount of arterial blood in the tissue during eachcardiac cycle.

Pulse oximeters typically utilize a non-invasive sensor that transmitselectromagnetic radiation, such as light, through a patient's tissue andthat photoelectrically detects the absorption and scattering of thetransmitted light in such tissue. One or more of the above physiologicalcharacteristics may then be calculated based upon the amount of lightabsorbed and scattered. More specifically, the light passed through thetissue is typically selected to be of one or more wavelengths that maybe absorbed and scattered by the blood in an amount correlative to theamount of the blood constituent present in the tissue. The measuredamount of light absorbed and scattered may then be used to estimate theamount of blood constituent in the tissue using various algorithms.

Pulse oximetry readings measure the pulsatile, dynamic changes in amountand type of blood constituents in tissue. Other events besides thepulsing of arterial blood may lead to modulation of the light path,direction, and the amount of light detected by the sensor, creatingerror in these measurements. Pulse oximetry measurements may be affectedby various noise sources, and various types of events may causeartifacts that may obscure the blood constituent signal. For example,signal artifacts may be caused by moving a sensor in relation to thetissue, by increasing or decreasing the physical distance betweenemitters and detectors in a sensor, by changing the direction ofemitters or detectors with respect to tissue or each other, by changingthe angles of incidence and interfaces probed by the light, by directingthe optical path through different amounts or types of tissue, or byexpanding, compressing or otherwise altering tissue near a sensor. Inthe emergency room, critical care, intensive care, and trauma centersettings, where pulse oximetry is commonly used for patient monitoring,the wide variety of sources of motion artifacts includes moving of apatient or the sensor by healthcare workers, physical motion of anunanaesthetised or ambulatory patient, shivering, seizures, agitation,response to pain and loss of neural control. These motions oftentimeshave similar frequency content to the pulse, and may lead to similar oreven larger optical modulations than the pulse.

Two categories of pulse oximetry sensors in common use may be classifiedby their pattern of use: the disposable and the reusable sensor.Disposable sensors are typically flexible bandage-type structures thatmay be attached to the patient with adhesive materials, providing acontact between the patient's skin and the sensor components. Disposablesensors have multiple advantages, including ease of conformation to thepatient. However, the flexible nature of disposable sensors renders themsusceptible to signal artifacts caused by mechanical deformation of thesensor, which changes the amount of light detected. Reusable sensors,often semi-rigid or rigid clip-type devices, are also vulnerable tosignal artifacts. Both categories of sensors may have modulations ofdetected light induced by the physical motion of the sensor componentswith respect to each other and the tissue.

Signal artifacts may sometimes be addressed by signal processing andfiltering to mitigate the effects of motion after the motion hasoccurred. However, signal processing algorithms to filter out motionartifacts after they have occurred may not filter out all type ofartifacts. For example, certain types of regular movements, such astapping, may not be interpreted by a signal artifact filter as noise.Thus, it would be desirable to provide a sensor that prevents, reducesthe occurrence of, or mitigates movements that may lead to motionartifacts. Such a sensor may incorporate elements which enhance patientcomfort without reducing the sensor's resistance to movement or outsideforces.

SUMMARY

Certain aspects commensurate in scope with the originally claimedinvention are set forth below. It should be understood that theseaspects are presented merely to provide the reader with a brief summaryof certain forms that the invention might take and that these aspectsare not intended to limit the scope of the invention. Indeed, theinvention may encompass a variety of aspects that may not be set forthbelow.

There is provided a sensor that includes: a sensor body comprising anelastic material; and an emitter and a detector disposed on the sensorbody, wherein sensor body is substantially inelastic in at least part ofa region of the sensor body connecting the emitter and the detector.

There is also provided a pulse oximetry system that includes: a pulseoximetry monitor; and a pulse oximetry sensor adapted to be operativelycoupled to the monitor. The sensor includes a sensor body comprising anelastic material; and an emitter and a detector disposed on the sensorbody, wherein sensor body is substantially inelastic in at least part ofa region of the sensor body connecting the emitter and the detector.

There is also provided a method that includes: applying a sensor bodycomprising an emitter and a detector to a patient's tissue; andstretching an elastic portion of a sensor body in response to a movementof the tissue, wherein the optical distance between the emitter and thedetector remains substantially fixed.

There is also provided a method of manufacturing a sensor that includes:providing a sensor body comprising an elastic material; and providing anemitter and a detector disposed on the sensor body, wherein sensor bodyis substantially inelastic in at least part of a region of the sensorbody connecting the emitter and the detector.

There is also provided a sensor that includes: a sensor body adapted toexpand in response to a biasing force; and an emitter and a detectordisposed on the sensor body, wherein the sensor body is adapted to fixthe optical distance between the emitter and the detector.

There is also provided a sensor that includes: a sensor body comprisingat least one elastic electronic component; and an emitter and a detectordisposed on the sensor body.

There is also provided a system that includes: a monitor; and a sensoradapted to be operatively coupled to the monitor, the sensor including:a sensor body comprising at least one elastic electronic component; andan emitter and a detector disposed on the sensor body.

There is also provided a method of response to movement of a sensor thatincludes: applying a sensor body comprising an emitter and a detector toa patient's tissue; and stretching an elastic electronic component of asensor body in response to a movement of the tissue, wherein the opticaldistance between the emitter and the detector remains substantiallyfixed.

There is also provided a method of manufacturing a sensor, including:providing a sensor body comprising at least one elastic electroniccomponent; and providing an emitter and a detector disposed on thesensor body.

There is also provided a sensor that includes: a sensor body; an emitterand a detector disposed on the sensor body; and an electronic componentoperatively connected to the emitter or the detector adapted to expandin response to a biasing force.

There is also provided a sensor that includes: a sensor body comprisingan exterior surface and a tissue-contacting surface; at least onesensing element disposed on the sensor body; a cable adapted to beelectrically coupled to the sensing element; and a cable guide disposedon exterior surface of the sensor body, wherein the cable guide isadapted to hold the cable in a predetermined position on the sensorbody.

There is also provided a pulse oximetry system that includes: a pulseoximetry monitor; and a pulse oximetry sensor adapted to be operativelycoupled to the monitor. The sensor includes: a sensor body comprising anexterior surface and a tissue-contacting surface; at least one sensingelement disposed on the sensor body; a cable adapted to be electricallycoupled to the sensing element; and a cable guide disposed on exteriorsurface of the sensor body, wherein the cable guide is adapted to holdthe cable in a predetermined position on the sensor body.

There is also provided a method that includes: applying a sensor bodycomprising a sensing component to a patient's tissue; and securing asensor cable that is operatively connected to the sensing component in apredetermined position on a sensor body with a cable guide.

There is also provided a method of manufacturing a sensor that includes:providing a sensor body comprising an exterior surface and atissue-contacting surface; providing at least one sensing elementdisposed on the sensor body; providing a cable adapted to beelectrically coupled to the sensing element; and providing a cable guidedisposed on the exterior surface of the sensor body, wherein the cableguide is adapted to hold the cable in a predetermined position on thesensor body.

There is also provided a sensor that includes: a sensor body; at leastone sensing element disposed on the sensor body; and a cable adapted tobe electrically coupled to the sensing element, wherein the cable isdisposed along the sensor body in a curvilinear configuration.

There is also provided a system that includes: a monitor; and a sensoradapted to be operatively coupled to the monitor. The sensor includes: asensor body; at least one sensing element disposed on the sensor body;and a cable adapted to be electrically coupled to the sensing element,wherein the cable is disposed along the sensor body in a curvilinearconfiguration.

There is also provided a method that includes: electrically coupling asensing element to a monitor with a cable, wherein sensing element isdisposed on the sensor body and wherein the cable is disposed along thesensor body in a curvilinear configuration.

There is also provided a method that includes: providing a sensor body;providing at least one sensing element disposed on the sensor body; andproviding a cable adapted to be electrically coupled to the sensingelement, wherein the cable is disposed along the sensor body in acurvilinear configuration.

There is also provided a sensor that includes: an emitter and a detectordisposed on a substantially rigid substrate, wherein the substantiallyrigid substrate is adapted to hold the emitter and detector at asubstantially fixed optical distance relative to one another when thesensor is applied to a patient.

There is also provided a system that includes: a monitor; and a sensoradapted to be operatively coupled to the monitor. The sensor includes:an emitter and a detector disposed on a substantially rigid substrate,wherein the substantially rigid substrate is adapted to hold the emitterand detector at a substantially fixed optical distance relative to oneanother when the sensor is applied to a patient.

There is also provided a method that includes: fixing the opticaldistance between an emitter and a detector relative to one another,wherein the emitter and the detector are disposed on a substantiallyrigid substrate.

There is also provided a method of manufacturing a sensor that includes:providing a substantially rigid substrate on which an emitter and adetector are disposed, wherein the substantially rigid substrate isadapted to hold the emitter and the detector at a substantially fixedoptical distance.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1A illustrates a cross-sectional view of an exemplary embodiment ofa transmission-type bandage-style sensor with an elastic sensor body;

FIG. 1B illustrates a top view of the sensor of FIG. 1A applied to apatient digit;

FIG. 1C illustrates a perspective view the sensor of FIG. 1A;

FIG. 1D illustrates a cross-sectional view of an alternative embodimentof a sensor using reflectance-type sensing elements;

FIG. 2A illustrates a cross-sectional view of an exemplary embodiment ofan elastic transmission-type bandage-style sensor applied to a patient'sdigit, whereby the sensor includes a stiffening member;

FIG. 2B illustrates a cross-sectional view of an exemplary embodiment ofan elastic reflectance-type bandage-style sensor applied to a patient'sdigit, whereby the sensor includes a stiffening member;

FIG. 2C illustrates an embodiment of the sensor of FIG. 2B, whereby thestiffening member and sensing components may be a unitary assembly;

FIG. 3A illustrates a cross-sectional view of an alternate exemplaryembodiment of a bandage-style sensor with an inelastic sensor body withelastic portions disposed proximate to the finger joint;

FIG. 3B illustrates a cross-sectional view of the sensor of FIG. 3A withthe finger joint flexed;

FIG. 4 illustrates a side view of an exemplary embodiment of a sensorwith an elastic sensor cable;

FIG. 5A illustrates a side view of an exemplary embodiment of a sensorwhereby the sensor cable is disposed along the side of the finger andsecured with a cable guide;

FIG. 5B illustrates a top view of the sensor of FIG. 5A;

FIG. 5C illustrates a perspective view of the sensor of FIG. 5A;

FIG. 6A illustrates a side view of an embodiment of an exemplary sensorapplied to a patient's finger with a sensor cable disposed on the sensorbody in a configuration that avoids the fingertip region;

FIG. 6B illustrates a perspective view of the sensor of FIG. 6A;

FIG. 7A illustrates a perspective view of an embodiment of an exemplarysensor with alignment indices for the sensor cable;

FIG. 7B illustrates a top view of the sensor of FIG. 7A applied to apatient's finger and secured with adhesive bandages such that the sensorcable is aligned with the alignment indices;

FIG. 8 illustrates a cross-sectional view of an embodiment of anexemplary sensor with a sensor cable that extends at an angle away fromthe sensor body;

FIG. 9 illustrates a side view of an embodiment of an exemplary sensorwith a flexible circuit connecting the emitter and detector; and

FIG. 10 illustrates a pulse oximetry system coupled to a multi-parameterpatient monitor and a sensor according to embodiments of the presentinvention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

In accordance with the present technique, sensors for pulse oximetry orother applications utilizing spectrophotometry are provided that reducesignal artifacts by reducing the occurrence of tissue deformation, suchas compression or discoloration, associated with the movement of apatient's tissue relative to the sensor or the movement of the sensorelements relative to one another. For example, sensors are providedherein that include elastic materials that may accommodate patientmovement. The sensors that include elastic materials are configured toreduce pressure from the sensor on the tissue during such movement.Sensors are also provided in which a sensor cable is directed orarranged in relation to the sensor body such that the pressure or weightof the cable on a patient's tissue is reduced.

Signal artifacts in pulse oximetry may be caused by patient movement,including movement of the optically probed tissue within the sensor.Although a typical conformable sensor may be sufficiently flexible towrap around a patient's tissue, such a flexible yet inelastic sensorwill nonetheless provide resistance to the tissue as it moves within thesensor. As a patient's tissue presses against an inelastic sensor'ssurfaces, such as the sensor body, the sensing elements, and the cable,the pressure of the sensor against the tissue may result in temporarychanges to the tissue. Such changes in response to pressure includeblanching of the skin, coloring of the skin due to blood pooling,creasing of the skin in response to bending at joints, and spreading orcompression of the tissue. These variations in tissue geometry and colormay result in signal artifacts. For example, coloring of the skin mayresult in increased absorption of light by the tissue that is notrelated to a physiological constituent. Alternatively, blanching of theskin may lead to shunting of light through exsanguinated or partiallyexsanguinated tissue. Additionally, although an inelastic sensor may notexpand or contract in response to patient movement, such a sensor mayyet be vulnerable to mechanical deformation that may change the geometryof the sensing elements relative to one another. As bandage-typeinelastic sensors are generally relatively flexible, though inelastic,such sensors may twist or come away from the skin, which may alter thegeometry of the sensing elements. Because medical sensors are often usedin settings where it is difficult to prevent patient motion, it isdesirable to provide a mechanism for reducing the effects of patientand/or sensor motion on the sensor signals.

Sensors are disclosed herein that include elastic materials and that mayreduce the effect of patient motion within a sensor. FIG. 1A illustratesa cross-sectional view of an exemplary bandage-type sensor 10Aappropriate for use on a patient's finger 12. The sensor 10A has anelastic sensor body 14. The elastic sensor body 14 may accommodatemovement of the finger 12 with the sensor 10A. An inelastic portion 15disposed on the sensor body in a region between the emitter 16 and thedetector 18 may serve to reduce or eliminate changes in the opticaldistance due to stretching of the elastic sensor body 14. The inelasticportion 15 does not stretch in response to the patient movement, andthus the accommodation of the patient movement by the elastic sensorbody 14 may have a reduced effect or no effect on the position of theemitter 16 and the detector 18 relative to one another, as discussed inmore detail below. As depicted, the finger 12 is flexed, causing theelastic sensor body 14 to stretch and expand, indicated by arrows 20, inan area corresponding to the nail side of the finger joint. In the areacorresponding to the palm side of the finger joint 22, the elasticsensor body may contract, as indicated by arrows 24. As shown in FIG.1B, a top view of the sensor 10A, the elastic sensor body 14 may alsostretch to accommodate spreading of the tissue in the fingertip regionof the finger during flexing, indicated by arrows 26. Alternatively, inother embodiments (not shown) the tissue in the fingertip region mayspread or expand when the finger 12 is pressed against a rigid object.Hence, as the finger 12 moves, the elastic sensor body 14 is able toconform to the tissue as it changes shape while the inelastic portion 15provides stability to the emitter 16 and the detector 18. FIG. 1C is atop view of the sensor 10A showing the inelastic portion 15 in theregion of the sensor body 14 between the emitter 16 and the detector 18.In an alternative embodiment, the sensor 10A may be a reflectance-typesensor, as shown in FIG. 1D. In such an embodiment, the emitter 16 andthe detector 18 are positioned side-by-side. Such a sensor may providecertain advantages. For example, the emitter 16 and the detector 18 maybe manufactured as a single, smaller part as compared to atransmission-type sensor.

The term elastic as used herein may describe any material that, uponapplication of a biasing force, is able to be stretched at least about100% (i.e., to a stretched, biased length that is at least about 100% ofits relaxed unbiased length). Many elastic materials may be elongated bymuch more than 400% and may, for example, be elongated at least 500%,600% or more. Further, upon release of the biasing force, the elasticmaterial is able to substantially recover its unbiased length. Incertain embodiments, upon release of the biasing force, the elasticmaterial returns to a length that is 120% or less of its originalunbiased length. For example, a hypothetical elastic material that isone inch in length is able to be stretched to at least 2.00 inches, andwhen the stretch is released, the material return to a length that isless than 1.20 inches. Exemplary elastic materials may include spandexor spandex blends. Another appropriate elastomer is Rx715P, availablefrom Scapa (Windsor, Conn.). In certain embodiments, it is contemplatedthat the elastic material may be a woven or knit material. In oneembodiment, the elastic material may be woven or otherwise configuredsuch that the material has a one-way stretch along a single axis. Forexample, a one-way elastic material may stretch lengthwise down thefinger over the joints as the finger is bent. In other embodiments, theelastic material may be an elastomer, such as a polymer-based material.Appropriate materials also include natural rubber, silicone rubber,neoprene, and synthetic polymers.

In certain embodiments, sensors that include elastic materials mayprovide a compressive force to the tissue to which they are applied. Thecompressive force provided by a sensor according to the presenttechniques can be varied to provide an appropriate level of pressure tothe tissue. In certain embodiments, a sensor including an elasticmaterial may provide sufficient pressure to the tissue so that theapplied pressure exceeds the typical venous pressure of a patient, butdoes not exceed the diastolic arterial pressure. A sensor that applies apressure greater than the venous pressure may squeeze excess venousblood from the optically probed tissue, thus enhancing the sensitivityof the sensor to variations in the arterial blood signal. Since thepressure applied by the sensor is designed to be less than the arterialpressure, the application of pressure to the tissue does not interferewith the arterial pulse signal. Typical venous pressure, diastolicarterial pressure and systolic arterial pressure are typically less than10-35 mmHg, 80 mmHg, and 120 mmHg, respectively, although thesepressures may vary because of the location of the vascular bed and thepatient's condition. In certain embodiments, the sensor may be adjustedto overcome an average pressure of 15-30 mmHg. In other embodiments, lowarterial diastolic blood pressure (about 30 mmHg) may occur in sickpatients. In such embodiments, the sensor may remove most of the venouspooling with light to moderate pressure (to overcome about 15 mmHg).

Sensors that include elastic materials as described herein may alsoinclude an inelastic portion 15 disposed on the sensor body that mayreduce or eliminate changes in optical distance between the sensingelements due to sensor bending or stretching in response to movement.The inelastic portion 15 may include any substantially inelasticmaterial and relatively inflexible material, including substantiallyinelastic stiffened paper, metal, or polymeric material. Generally, asubstantially inelastic portion is unable to be elongated 50% or more ofits total length. Thus, a hypothetical inelastic material one inch inlength is not able to be stretched elastically to 1.50 inches or morewithout causing damage or permanent deformation to the material.

The inelastic portion 15 may provide stability to the emitter 16 anddetector 18 by mitigating the effects of stretching the elastic sensorbody 14 on the optical distance. Reducing or controlling changes in theoptical distance may include reducing any change in position or geometryof the sensing elements of a sensor. More specifically, a change inoptical distance may involve any change in optical geometry, such as achange in the path length, a change in the relative angle of the sensingelements relative to one another, and/or a change in the angle of thesensing elements relative to the tissue. As sensors do not typicallyemit nor detect light omnidirectionally, any motions that lead tovariations in angle of sensor components may alter the amount of lightdetected, and may force detected light through different portions oftissue. In any case, variability in the optical path length can causesignal artifacts and obscure the desired pulse oximetry signal. Thus, itis desirable that a sensor's emitter(s) and detector(s) experience aminimum of movement relative to one another and relative to thepatient's tissue.

In an alternate embodiment, a cross-sectional view of an elastic sensor10B is illustrated in FIG. 2A in which an inelastic portion of thesensor 10B includes a stiffening member 28. The stiffening member 28 isdisposed on an elastic sensor body 14 in a region between the emitter 16and detector 18. The stiffening member 28 may be constructed from anysuitable material that functions to hold the emitter 16 and the detector18 at a substantially fixed optical distance when the sensor 10B isapplied to a patient. For example, a suitable stiffening member 28 maybe metal, plastic or polymeric material, or cardboard. In certainembodiments, suitable metals include aluminum or brass. The stiffeningmember 28 may be in the shape of a strip, wire, or mesh that can beeasily adapted for use with an elastic sensor body 14. The stiffeningmember 28 may adapted to be bent, shaped, activated, or applied to aconformable elastic sensor body 14 in order to hold an emitter 16 and adetector 18 at a substantially fixed optical distance. The stiffeningmember 28 may be sized to form a strip that is generally in the areasurrounding the emitter 16 and the detector 18. A stiffening member 28need not be solid, but may also be a fluid or other non-solid materialthat stabilizes the optical distance between an emitter 16 and adetector 18. For example, a stiffening member 28 may include a bladderthat is adapted to hold a fluid. In certain embodiments, it may bedesirable employ a gas or gas mixture as part of the stiffening member28 for reasons related to cost, manufacturing convenience, and totalsensor weight.

FIG. 2B illustrates an embodiment in which the sensor 10B is configuredto be in reflectance mode. In certain embodiments, the emitter 16 andthe detector 18 may both be disposed on or within the stiffening member28, as shown in FIG. 2C. In FIG. 2C, a sensing component assembly 25 isformed by the emitter 16 and detector 18, which are embedded in thestiffening member 28 and are connected to a cable 31 by wires 29. Thesensing component assembly 25 may be disposed on the elastic sensor body14, adhesively or otherwise. In an alternate embodiment (not shown), thesensing component assembly 25 may be applied to a patient's tissue withelastic tape or bandages.

In certain embodiments, a sensor may include elastic materials only inspecific portions of the sensor. For example, it may be desirable todesign a finger sensor with elastic portions that correspond to areas ofa finger that are likely to move, such as joints. FIG. 3A illustrates abandage-type sensor 10C applied to a patient's finger 30. The sensor 10Cincludes an elastic portion 32 disposed on an inelastic sensor body 34.The elastic portion 32 corresponds to the top of a finger joint 31. Asdepicted in FIG. 3B by arrows 33, when the finger 30 bends at the joint31, the elastic portion 32 stretches to accommodate the movement.However, the optical distance, indicated by dashed line “D”, between theemitter 16 and the detector 18 remains substantially fixed.

It should be understood the ratio of elastic portions and inelasticportions of a sensor body may be varied according to the activity levelof the patient wearing the sensor. For example, for a very activepatient, it may be advantageous to apply a sensor having more elasticportions, such as a ratio of elastic portions to inelastic portions ofgreater than one. In certain embodiments, it is contemplated that totalelastic surface area of a sensor body may be at least about 5%, andtypically in a range from about 10% to about 95%.

In certain embodiments, a sensor may include elastic electricalcomponents, including sensor cable components or wires. FIG. 4illustrates a side view of a sensor 10D with an elastic cable 37disposed on the sensor body 35. As the finger flexes, the elastic cable37 is able to accommodate the flexing motion. The elastic elasticcomponents, such as the elastic cable 37, may include transducers and/orelectronic circuits integrated onto an elastic polymer that includeelastic metal that remain electrically conducting even under large andrepeated stretching and relaxation. Suitable elastic polymeric materialsinclude silicone rubber, such as polydimethyl siloxane (PDMS) andacrylic rubber. Electrically conductive materials useful for elasticconductive films include metallic conducting materials such as copper,silver, gold, aluminum and the like. Alternatively, electricallyconductive materials include organic conducting materials such aspolyaniline. Suitable electrically conductive materials include asemiconductor, either inorganic like silicon or indium tin oxide, ororganic-like pentacene or polythiophene. Alternatively, the electricallyconductive materials can be alloys instead of stoichiometric elements orcompounds. The elastic conductive film can be formed on elasticpolymeric substrate by electron beam evaporation, thermal evaporation,sputter deposition, chemical vapor deposition (CVD), electroplating,molecular beam epitaxy (MBE) or any other conventional means.

Sensors are also disclosed herein in which a sensor cable is routed awayfrom areas of the sensor body that may be subject to tissue pressure ormovement. Typically, a sensor cable is embedded in the sensor body andruns through the sensor body along an imaginary axis connecting thesensor's emitter and detector. When such a sensor is applied to apatient's finger, the cable wraps around the fingertip region and runsalong the top of the digit. As the finger flexes, the relatively rigidand inelastic cable resists the flexing motion, which may result intissue discoloration, such as reddening or exsanguinations, ordeformation in the area where the tissue pushes against the cable.Similarly, when the finger taps against a rigid object, the fingertipregion is pushed against the relatively rigid sensor cable, and thetissue may experience discoloration or deformation. As changes in tissuecolor and geometry may lead to signal artifacts, it is desirable toalter the arrangement of the sensor cable in relation to the sensor bodyto mitigate such signal interference.

Sensors are provided herein that include cables with non-axial orcurvilinear paths in relation to the sensor body. FIG. 5A illustrates aside view reflectance-type sensor 10E applied to a patient's finger 46.FIG. 5B is a top view of the sensor 10E. The emitter 40 and the detector42 are operatively connected to a sensor cable 44. The sensor cable 44,rather than wrapping around the tip of the finger 46, follows anonlinear, i.e. non-axial, route within the sensor body 48. The cable 44is partially embedded in the sensor body 48, and may emerge from thesensor body 48 at a site 50 that is not on the outer perimeter 52.Alternatively, the site 50 may be along the outer perimeter 52. When thecable 44 emerges from the sensor body 48, it may be wrapped around thetop of the finger 46 and secured with a cable guide 54, as shown in FIG.5B. The cable guide 54 may be any suitable securing mechanism, include aloop, slot, snap, adhesive, or hook and loop fastener. Further, thecable guide 54 may be elastic in certain embodiments, allowing it tostretch tightly over the cable 44 to provide a secure hold.

Generally, the cable 44 may be routed along the sensor body 48 in anyconfiguration associated with a mitigation of signal artifacts. Forexample, the cable 44 may be routed along the sensor body 48, e.g.embedded within or disposed on a surface of the sensor body 48, to avoidthe region 56 of the sensor body 48 corresponding with the fingertipregion of the finger in order to mitigate signal artifacts associatedwith scratching or tapping. In order to mitigate motion artifactsassociated with bending at a joint, the cable 44 may routed along thesensor body 48 to avoid the most dynamic regions of the finger 46, suchas the top and bottom of the joint. In such an embodiment, the cable 44may be routed in an area corresponding to side regions 58 and 60 of thefinger 46, as shown in FIG. 5C. It should be understood that in anotherembodiment, the cable may be routed along the sensor body in an areacorresponding to side regions 58A and 60A, corresponding to analternative side of the finger.

Such an arrangement of the sensor cable may also be advantageous in atransmission-type sensor, in which a sensor's emitter 62 and detector 64lie on opposing side of the tissue. FIG. 6A illustrates a sensor 10F ofthis type applied to a patient's finger 61. Wire leads 68 from anemitter 62 and a detector 64 converge at a sensor cable 66. FIG. 6Billustrates a perspective view of the sensor 10F. The wire leads 68 andsensor cable 66 are arranged along the sensor body 70 such that thesensor cable 66 is not disposed within a region 72 of the sensor body 70corresponding with the fingertip region of the finger 61 in order tomitigate signal artifacts associated with scratching or tapping. Thecable 66 may be wrapped around the finger 61 and secured with a cableguide 74. In an alternate embodiment (not shown), the wire leads 68,which are relatively thin, may be arranged to run along the fingertipregion 72 and then along the sensor body 70 to join the sensor cable 66,which is not disposed in the fingertip region 72.

In certain embodiments, it may be advantageous for a sensor cable to besecured by a healthcare worker with tape or bandages on an appropriatelocation of a sensor body. FIG. 7A illustrates a sensor 10G whichincludes alignment indices 76 for a sensor cable 77 on a non-tissuecontacting surface 78 of the sensor body 80. FIG. 7B shows the sensor10G applied to a patient's finger 82. When the sensor 10G is applied,the sensor cable 77 may be arranged along the non-tissue contactingsurface 78 of the sensor body 80 by a healthcare worker. The alignmentindices 76 provide an indication where the sensor cable 77 should lieagainst the sensor body 80 prior to being secured by bandages 81, asshown, or by tape or other securing mechanisms. Alternatively, thehealthcare worker may wish to wrap the sensor cable 77 along the sensorbody 80 in such a manner as to minimize the pressure of the sensor cable77 against the patient's finger 82. In such an embodiment (not shown),the sensor cable 77 may be loosely wrapped such the sensor cable 77 isnot flush against the sensor body 80.

FIG. 8 illustrates a sensor 10J with an alternate sensor cableconfiguration. The sensor cable 114 is electrically connected to theemitter 110 and detector 112 by wire leads 113. The wire leads 113 jointhe sensor cable 114 within the sensor body 108, and the sensor cable114 emerges from the sensor body 108 at an angle that is not in linewith the plane of the sensor body 108 when the sensor body 108 is laidflat. Although the sensor body 108 generally assumes a more complex,nonplanar geometry after application to a patient's tissue, the resultof this configuration is that the sensor cable 114 is directed away fromthe tissue. Thus, the sensor cable 114 may be less likely to interferewith patient motion or to compress the tissue. Such a configuration maybe applied to the patient's tissue in any configuration. For example,the sensor 10J may be applied such that the sensor cable 114 emergesfrom the sensor body 108 along the sides of the patient's finger. Insuch an embodiment, the sensor cable 114 emerges and is at an angle suchthat the sensor cable 114 is not flush against the tissue.

In another embodiment, it may be advantageous to replace all or part ofa sensor cable with a lightweight flexible circuit. FIG. 9 illustratesan exemplary sensor 101 that includes a flexible circuit 82 electricallyconnecting the emitter 84 and the detector 86 to a sensor cable 88. Theflexible circuit 82 includes conductive elements printed on a flexible,non-conductive substrate, such as polyimide or polyester, in order toprovide electrical communication to and from the emitter 84 and thedetector 86. The flexible circuit 82 may be embedded in the sensor body90 in a region between the emitter 84 and the detector 86. As shown inFIG. 8, the flexible circuit 82 bends easily around the finger 83. Asthe flexible circuit 82 has few rigid surfaces, the tissue mayexperience fewer discoloration or deformation events associated withsignal artifacts when pressed against the flexible circuit 82 embeddedin the sensor body 90. The flexible circuit 82 may include at least oneconnection point that is suitable for electrically coupling the flexiblecircuit 82 to the sensor cable 88.

A sensor, illustrated generically as a sensor 10, may be used inconjunction with a pulse oximetry monitor 92, as illustrated in FIG. 10.It should be appreciated that the cable 94 of the sensor 10 may becoupled to the monitor 92 or it may be coupled to a transmission device(not shown) to facilitate wireless transmission between the sensor 10and the monitor 92. The monitor 92 may be any suitable pulse oximeter,such as those available from Nellcor Puritan Bennett Inc. Furthermore,to upgrade conventional pulse oximetry provided by the monitor 92 toprovide additional functions, the monitor 92 may be coupled to amulti-parameter patient monitor 96 via a cable 98 connected to a sensorinput port or via a cable 100 connected to a digital communication port.

The sensor 10 includes an emitter 102 and a detector 104 that may be ofany suitable type. For example, the emitter 102 may be one or more lightemitting diodes adapted to transmit one or more wavelengths of light inthe red to infrared range, and the detector 104 may one or morephotodetectors selected to receive light in the range or ranges emittedfrom the emitter 102. Alternatively, an emitter may also be a laserdiode or a vertical cavity surface emitting laser (VCSEL). An emitterand detector may also include optical fiber sensing elements. An emittermay include a broadband or “white light” source, in which case thedetector could include any of a variety of elements for selectingspecific wavelengths, such as reflective or refractive elements orinterferometers. These kinds of emitters and/or detectors wouldtypically be coupled to the rigid or rigidified sensor via fiber optics.Alternatively, a sensor may sense light detected from the tissue is at adifferent wavelength from the light emitted into the tissue. Suchsensors may be adapted to sense fluorescence, phosphorescence, Ramanscattering, Rayleigh scattering and multi-photon events or photoacousticeffects. For pulse oximetry applications using either transmission orreflectance type sensors the oxygen saturation of the patient's arterialblood may be determined using two or more wavelengths of light, mostcommonly red and near infrared wavelengths. Similarly, in otherapplications, a tissue water fraction (or other body fluid relatedmetric) or a concentration of one or more biochemical components in anaqueous environment may be measured using two or more wavelengths oflight, most commonly near infrared wavelengths between about 1,000 nm toabout 2,500 nm. It should be understood that, as used herein, the term“light” may refer to one or more of ultrasound, radio, microwave,millimeter wave, infrared, visible, ultraviolet, gamma ray or X-rayelectromagnetic radiation, and may also include any wavelength withinthe radio, microwave, infrared, visible, ultraviolet, or X-ray spectra.

The emitter 102 and the detector 104 may be disposed on a sensor body106, which may be made of any suitable material, such as plastic, foam,woven material, or paper, and may include elastic portions.Alternatively, the emitter 102 and the detector 104 may be remotelylocated and optically coupled to the sensor 10 using optical fibers. Inthe depicted embodiments, the sensor 10 is coupled to a cable 94 that isresponsible for transmitting electrical and/or optical signals to andfrom the emitter 102 and detector 104 of the sensor 10. The cable 94 maybe permanently coupled to the sensor 10, or it may be removably coupledto the sensor 10—the latter alternative being more useful and costefficient in situations where the sensor 10 is disposable.

The sensor 10 may be a “transmission type” sensor. Transmission typesensors include an emitter 102 and detector 104 that are typicallyplaced on opposing sides of the sensor site. If the sensor site is afingertip, for example, the sensor 10 is positioned over the patient'sfingertip such that the emitter 102 and detector 104 lie on either sideof the patient's nail bed. In other words, the sensor 10 is positionedso that the emitter 102 is located on the patient's fingernail and thedetector 104 is located 180° opposite the emitter 102 on the patient'sfinger pad. During operation, the emitter 102 shines one or morewavelengths of light through the patient's fingertip and the lightreceived by the detector 104 is processed to determine variousphysiological characteristics of the patient. In each of the embodimentsdiscussed herein, it should be understood that the locations of theemitter 102 and the detector 104 may be exchanged. For example, thedetector 104 may be located at the top of the finger and the emitter 102may be located underneath the finger. In either arrangement, the sensor10 will perform in substantially the same manner.

Reflectance type sensors also operate by emitting light into the tissueand detecting the light that is transmitted and scattered by the tissue.However, reflectance type sensors include an emitter 102 and detector104 that are typically placed on the same side of the sensor site. Forexample, a reflectance type sensor may be placed on a patient's fingeror forehead such that the emitter 102 and detector 104 lie side-by-side.Reflectance type sensors detect light photons that are scattered back tothe detector 152. A sensor 10 may also be a “transflectance” sensor,such as a sensor that may subtend a portion of a patient's heel.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Indeed, the presenttechniques may not only be applied to measurements of blood oxygensaturation, but these techniques may also be utilized for themeasurement and/or analysis of other blood and/or tissue constituentsusing principles of pulse oximetry. For example, using the same,different, or additional wavelengths, the present techniques may beutilized for the measurement and/or analysis of carboxyhemoglobin,methemoglobin, total hemoglobin, fractional hemoglobin, intravasculardyes, hematocrit, carbon dioxide, carbon monoxide, protein, lipid and/orwater content or compartmentalization. Rather, the invention is to coverall modifications, equivalents, and alternatives falling within thespirit and scope of the invention as defined by the following appendedclaims.

1. A sensor comprising: a conformable bandage-type sensor bodyconfigured to be applied to a digit; at least one sensing elementdisposed on the sensor body; and a cable adapted to be electricallycoupled to the sensing element, wherein the cable is disposed along thesensor body in a curvilinear configuration and wherein the cable emergesfrom the sensor body at a site not on the outer perimeter of the sensorbody.
 2. The sensor, as set forth in claim 1, wherein the sensorcomprises at least one of a pulse oximetry sensor or a sensor formeasuring a water fraction.
 3. The sensor, as set forth in claim 1,wherein the sensor comprises a cable guide adapted to hold the cable inthe curvilinear configuration.
 4. The sensor, as set forth in claim 1,wherein the cable is embedded in the conformable bandage-type sensorbody in a curvilinear configuration.
 5. The sensor, as set forth inclaim 1, wherein the cable emerges from the conformable bandage-typesensor body at an angle not in line with a plane along a tangent line ofa surface of the conformable bandage-type sensor body at a point wherethe cable emerges from the conformable bandage-type sensor body.
 6. Thesensor, as set forth in claim 1, wherein the sensor comprises areflectance-type sensor.
 7. The sensor, as set forth in claim 1, whereinthe sensor comprises a transmission-type sensor.
 8. A system comprising:a monitor; and a sensor adapted to be operatively coupled to themonitor, the sensor comprising: a conformable bandage-type sensor bodyconfigured to be applied to a digit; at least one sensing elementdisposed on the conformable bandage-type sensor body; and a cableadapted to be electrically coupled to the sensing element, wherein thecable is disposed along the conformable bandage-type sensor body in acurvilinear configuration and wherein the cable emerges from the sensorbody at a site not on the outer perimeter of the sensor body.
 9. Thesystem, as set forth in claim 8, wherein the sensor comprises at leastone of a pulse oximetry sensor or a sensor for measuring a waterfraction.
 10. The system, as set forth in claim 8, wherein the sensorcomprises a cable guide adapted to hold the cable in the curvilinearconfiguration.
 11. The system, as set forth in claim 8, wherein thecable is embedded in the conformable bandage-type sensor body in acurvilinear configuration.
 12. The sensor, as set forth in claim 8,wherein the cable emerges from the conformable bandage-type sensor bodyat an angle not in line with plane along a tangent line of a surface ofthe conformable bandage-type sensor body at a point where the cableemerges from the conformable bandage-type sensor body.
 13. The system,as set forth in claim 8, wherein the sensor comprises a reflectance-typesensor.
 14. The system, as set forth in claim 8, wherein the sensorcomprises a transmission-type sensor.
 15. A method comprising:electrically coupling a sensing element to a monitor with a cable,wherein sensing element is disposed on a conformable bandage-type sensorbody configured to be applied to a digit and wherein the cable isdisposed along the conformable bandage-type sensor body in a curvilinearconfiguration and wherein the cable emerges from the sensor body at asite not on the outer perimeter of the sensor body.
 16. The method, asset forth in claim 15, wherein the sensor comprises a cable guideadapted to hold the cable in the curvilinear configuration.
 17. Themethod, as set forth in claim 15, wherein the cable is embedded in theconformable bandage-type sensor body in a curvilinear configuration. 18.A method of manufacturing a sensor, comprising: providing a conformablebandage-type sensor body configured to be applied to a digit; providingat least one sensing element disposed on the conformable bandage-typesensor body; and providing a cable adapted to be electrically coupled tothe sensing element, wherein the cable is disposed along the conformablebandage-type sensor body in a curvilinear configuration and wherein thecable emerges from the sensor body at a site not on the outer perimeterof the sensor body.
 19. The method, as set forth in claim 18, whereinthe sensor comprises a cable guide adapted to hold the cable in thecurvilinear configuration.
 20. The method, as set forth in claim 18,wherein the cable is embedded in the conformable bandage-type sensorbody in a curvilinear configuration.
 21. The method, as set forth inclaim 18, wherein the cable emerges from the conformable bandage-typesensor body at an angle not in line with plane along a tangent line of asurface of the conformable bandage-type sensor body at a point where thecable emerges from the conformable bandage-type sensor body.